The present invention relates generally to a throttle valve position control system for an internal combustion engine, in which an electrically or electromagnetically operable throttle valve actuator is employed for controlling the throttle valve angular position depending upon the degree of depression of an accelerator pedal. More particularly the invention relates to a throttle valve position control system which can control the throttle valve angular position depending not only on the accelerator pedal depression but also the difference between the actual output speed of the engine and the desired output speed for optimization of engine performance.
Such throttle valve position control systems have been disclosed in European Patent First Publications Nos. 01 14 401, 01 21 937, 01 21 938, and 01 21 939. In these prior proposals or developments, the throttle valve angular position is generally controlled by an electromagnetic actuator associated with the throttle valve. A throttle control signal is produced depending upon the degree of depression of an accelerator pedal as indicated by a signal generated at the accelerator pedal.
A similar throttle control system has also been disclosed in Japanese Patent First Publication (Tokkai) Showa No. 56-107925, published on Aug. 27, 1981. This document discloses an electronic fuel injection control system for a spark ignition internal combustion engine, which includes a throttle valve servo mechanism operative to control a throttle valve angular position depending upon the degree of depression of an accelerator pedal.
The aforementioned control systems are capable of controlling the throttle valve to a desired angular position corresponding to the depression rate of the accelerator pedals. Therefore, those systems may successful in controlling air induction at a rate corresponding to the accelerator depression degree. Theoretically, control of the throttle valve angular position implies direct control of engine output to obtain desired engine performance. However, in practice, due to production errors among individual engines and the wide range of possible environmental conditions, engine output does not necessarily correspond to the demand on the engine throughout the range of throttle valve angular positions.
There have been proposals for controlling engines or power trains including the engine and a power transmission to obtain output torque precisely corresponding to the output demand. SAE Technical Paper 830423, by the Society of Automotive Engineering, discloses a power train control system controlling the engine in a discrete manner by controlling the power transmission. In controlling the engine, the engine controller detects data from various points in the engine and adjusts fuel supply, ignition timing, EGR flow rate and intake air flow rate to optimal values derived from computations on the detected data. In controlling the transmission, a transmission controller detects engine load and vehicle speed, and derives the gear ratio to be established by the transmission and performs lock-up control on the basis of the results of computations on the detected data.
Another important factor in overall vehicle performance is good response of the driving torque to depression of the accelerator pedal. Specifically, in order to obtain good engine response characteristics to the accelerator pedal position, the output torque produced by the engine must precisely correspond at all times to that demanded manually by means of the accelerator pedal.
However, in practice, the engine output torque transmitted to the vehicular driving wheels tends to fluctuate due to environmental conditions and/or production errors. For example, it is notorious that engine output characteristics fluctuate significantly, even to a disturbing extent, as the engine warms up from a cold-weather start. Furthermore, many vehicles suffer shift-shock during shifting of the automatic power transmission due to deviations in engine speed and thus of engine output. This also degrades not only handling but also riding comfort.
Therefore, it would be desirable for the vehicular power train to provide uniform accelerator response so as to constantly produce an optimal engine output speed at every accelerator position and in every transmission gear position.